Deducting the sum of all elements in an array from the initial value

Question

Deducting the sum of all elements in an array from the initial value

In my current project, I am working with an array of objects structured as follows:

let budgetData = [{title: "Monthly Income", amount: "2500"}, {title: 
"rent", amount: "1000"},{title: "car", amount: "200"}];

I have been attempting to perform some calculations using this data set:

2500 - 1000 - 200 = whatever the result may be. You have the flexibility to keep adding more amounts to the array based on your monthly expenses.

Initially, when you run this calculation with just two values, the outcome matches expectations (e.g., 2 - 1 = 1).

However, if you add more than two amounts to the array, it seems that only the last value is being subtracted from the first one, impacting the accuracy of the final result (e.g., 5 - 2 - 1 = 4).

let amount = [];

for (let i = 1; i < budgetData.length; i++){ amount = 
budgetData[0].amount - budgetData[i].amount;

console.log(amount) === 2300

Despite running the above code with the provided information, the calculated answer turns out to be 2300 instead of the expected 1300.

I would appreciate some insights on where I might be making a mistake in my approach. Additionally, I am curious to know if there exists a built-in math function that can assist me in achieving the desired outcome efficiently.

javascript arrays for-loop math

Answer 1

Answer №1

Every iteration of the loop results in discarding the previous calculation and replacing amount with a new one. Ultimately, this leads to subtracting the final number from the initial number.

To avoid this, you should maintain a cumulative total, like so:

let budgetData = [
  {title: "Monthly Income", amount: "2500"}, 
  {title: "rent", amount: "1000"},
  {title: "car", amount: "200"}
];

let amount = budgetData[0].amount;

for (let i = 1; i < budgetData.length; i++){ 
   amount = amount - budgetData[i].amount;
}

console.log(amount);

Answer 2

Every iteration of the loop results in discarding the previous calculation and replacing amount with a new one. Ultimately, this leads to subtracting the final number from the initial number.

To avoid this, you should maintain a cumulative total, like so:

let budgetData = [
  {title: "Monthly Income", amount: "2500"}, 
  {title: "rent", amount: "1000"},
  {title: "car", amount: "200"}
];

let amount = budgetData[0].amount;

for (let i = 1; i < budgetData.length; i++){ 
   amount = amount - budgetData[i].amount;
}

console.log(amount);

Answer 3

Answer №2

Another approach is to decrease the array size:

const finalAmount = expensesData.reduce((first, second) => (first.amount || first) - second.amount);

In case your expense objects have a valueOf method defined like this:

 class Expense {
  constructor(attributes){
     Object.assign(this, attributes);
  }
  valueOf(){ return this.amount;}
}

expensesData = expensesData.map(item => new Expense(item));

The code becomes even more elegant:

const finalAmount = expensesData.reduce((x,y) => x-y);

Answer 4

Another approach is to decrease the array size:

const finalAmount = expensesData.reduce((first, second) => (first.amount || first) - second.amount);

In case your expense objects have a valueOf method defined like this:

 class Expense {
  constructor(attributes){
     Object.assign(this, attributes);
  }
  valueOf(){ return this.amount;}
}

expensesData = expensesData.map(item => new Expense(item));

The code becomes even more elegant:

const finalAmount = expensesData.reduce((x,y) => x-y);

Deducting the sum of all elements in an array from the initial value

Answer №1

Answer №2

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